Polymer films are perhaps one of the most common materials used for packaging. The films may be used, for instance, to package products such as various articles of manufacture and food items. Food items that are packaged by polymer films, for instance, include not only solid foods, but liquids such as drinks as well.
In some applications, the polymer film is coated with a metal in order to form a laminate that may be used as a packaging material or may be used in various other applications. For instance, metallized polymer films are also used as labels, decals, solar window films, decorative products, and microfilm in addition to being used in packaging applications. Of particular advantage, polymer films coated with a metallic layer prevent the passage of visible and ultraviolet light, which may serve to prevent oxidative degradation of a product covered by the film laminate.
In one particular embodiment, the metal layer is coated on a polyester film. When containing a metal layer, the polyester film provides a strong and flexible packaging material with desirable oxygen and moisture barrier properties in addition to having visible and ultraviolet light barrier properties. Of particular advantage, the metal coated polyester film is typically much less expensive to manufacture and use in packaging structures than conventional metallic foil.
In view of the above, those skilled in the art have attempted to devise various processes for bonding metal layers to polymer films, such as polyester films. For example, U.S. Pat. No. 4,493,872 to Funderburk, Culbertson and Posey discloses a polyester film coated with a copolyester that is designed to improve bonding between a metal layer and the polyester film. The processes and products disclosed in the '872 patent, which is incorporated herein by reference, have represented great advancements in the art. In fact, products made according to the '872 patent have experienced significant commercial success. For instance, metallized polyester films made according to the '872 patent are used to package many consumer products, such as many fruit beverage drink pouches.
The present disclosure is directed to further improvements in polymer film laminates that contain a metal or metal oxide layer. In particular, the present inventor (who is also listed as a co-inventor on the '872 patent) has discovered a specific copolyester film coating that further improves bonding between a polymer film layer and a metal layer.